1. Field of the Invention
The present invention relates to a photographic printing method for printing a film image onto photographic paper.
2. Description of the Related Art
It is empirically known that the ratios of transmittance of the three colors of light, blue (B), green (G), and red (R) transmitted through the overall image plane of a color negative on which a standard scene has been photographed occur, in general, at a substantially fixed rate. Printing conditions are determined in such a manner that a color obtained by integrating and mixing, with respect to the entire image plane, the densities of an image printed on color photographic paper by the transmitted light becomes gray or assumes a fixed hue, close to gray. For this reason, in an automatic printer the amount of light for printing (i.e., exposure amount) is determined on the basis of the following formula: EQU logEj=Kj+Dj (1)
where logE is a logarithm of an amount of light for printing; K is a constant; D is a large area transmittance density (LATD) of the negative measured by a photometric system; and j is the light of any one of the colors B, G and R.
However, if the quantity of light for printing is controlled in an automatic printer on the basis of the aforementioned Formula (1), the overall density of a print from an underexposed negative on which a gray subject has been photographed becomes high in comparison with a print from an adequately exposed negative, while the density of a print from overexposed tricolor normalized data becomes low. For this reason, the exposure amount is determined by means of a slope control function so as to correct Dj in Formula (1). Meanwhile, in an automatic printer provided with the slope control function such as the one described above, an improper color balance is liable to occur in color reproduction, and a faulty print in which the color balance is inappropriate is hence liable to occur in the case of negatives photographed with a non-natural light source (fluorescent lamp, tungsten lamp, or the like) substantially different from daylight, negatives in which color failures have occurred, and other similar negatives. For this reason, Dj in Formula (1) is further corrected (color corrected) so as to determine the exposure amount. With respect to normal correction, an overcorrection is referred to as a high correction, and an undercorrection is referred to as a low correction.
By automatically correcting the exposure amount for printing as described above, it is possible to efficiently produce prints of good final print quality by correcting improper color balance in the color reproduction of a negative using a different type of light source and improper color balance in color reproduction caused by a change in film characteristics (performance change due to the extended storage of film or variations in processing, etc.).
However, since the above described photograhic printing method is premised on the uniform finishing of prints, a problem exists in that it is impossible to cause the hues of a subject illuminant and a photographer's picture-taking intent in expressing the hues of the original scene to be reflected on the print. For instance, an evening scene is undesirably converted to a broad daylight scene. To resolve this problem, it suffices to determine the exposure amount by means of a lowered correction, but the final print quality deteriorates since it is impossible to correct the improper color balance in color reproduction caused by a change in film characteristics.
Meanwhile, the print exposure amount at the time of printing a film image onto photographic paper is determined by the amount of light received by the film from the subject at the time of photographing, and differs for each frame. In order to obtain prints of good color reproducibility, correction of a print exposure amount corresponding to photographing conditions becomes necessary. For this reason, the photographing light quality and the light quantity of a light source are recorded outside of the image plane of the film, and the print exposure amount is corrected on the basis of these items of information (Japanese Patent Application Laid-Open Nos. 51-117632 and 52-13333). However, it is impossible to completely remove the light emitted from the background (e.g. a red curtain or blue sky), and information on the photographing light quality can change depending on development conditions and the like. Hence, there exists a problem in that it is impossible to accurately estimate the light quality, and color reproducibility consequently deteriorates due to a change in the light quality of the subject illuminant. In addition, Japanese Patent Application Laid-Open Nos. 59-214023 and 64-6933 disclose techniques in which data such as the shutter speed, aperture, date, time, place, title, whether or not the photograph was taken with a different type of light source, and so forth are recorded on the film so as to be utilized in determination of print exposure amount. With these techniques, however, since an algorithm for estimating the light quality of the subject illuminant has not been developed, it is impossible to accurately estimate the light quality, and there occurs the same problem as that described above. Furthermore, the determination of the light quality of a subject illuminant can also be determined by the operator of the printer. However, in order to improve the determining accuracy, long experience is necessary, and only the tungsten light which is easy to determine is, in practice, detected.
An additional task lies in improving the accuracy of determination in cases where a film is exposed at a place distant from the place for producing prints, as when a film photographed overseas is printed in the U.S.
Another photographic printing, method is conventionally known in which the average image dens multiplicity of frames (e.g., the frames of one roll of film) is calculated, and by using this average image density, the print exposure amount is determined on the basis of, for instance, the following Formula (2) so as to print the film images onto photographic paper: EQU logEj=Sj{Cj(dj-dwj)+dwj}+Kj (2)
where EQU dj=Dj-ADj (3) ##EQU1## where j integer selected from 1-3, representing any one of red (R), green (G) and blue (B)
Dj: image density (e.g., an average density of the entire image plane) of an individual film image frame PA1 ADj: average image density (e.g., an average image plane density) of a multiplicity of film frames PA1 Sj: slope control value PA1 Cj: color correction value PA1 Kj: constant dependent on the printer, film, and photographic paper characteristics PA1 Ej: exposure control value corresponding to printing light quantity
According to this method, since average image densities are used, the amount of density information is large, and it is possible to obtain prints of good color reproducibility as compared with cases where the print exposure amount is simply determined for each frame. With this method, if an average image density deviates substantially from a standard density, prints of good color reproducibility cannot be obtained, so that image densities of frames photographed under extremely different light sources, image densities of frames deviating substantially from gray, and other similar image densities are not used for the calculation of the average image density.
Conventionally, however, since the influence of the quality of light illuminating the subject is not sufficiently removed, average image densities of sufficient accuracy have yet been obtained. For instance, if consideration is given to electronic flashes, the color temperature of the light of electronic flashes and reciprocity law failure characteristics of films are not normalized and differ depending on products. Photographs taken using electronic flashes account for as much as 40% of the total number of shots on average. Accordingly, color reproducibility deteriorates if frames photographed without using an electronic flash are subjected to print exposure the use of an average image density including numerous image densities of frames photographed by using the electronic flash.